1. Field of the Invention
The invention relates to a pointing device which is generally used to generate coordinates of position, more particularly to an electric circuit which is to be incorporated in a pointing device so as to reduce the energy consumption of the pointing device.
2. Description of the Related Art
A pointing device, such as a computer mouse, is used in combination with a data processing system, such as a computer, and is a useful and handy tool in determining and in generating coordinates of position so as to move a cursor on a computer display screen. The computer mouse generally comprises a movable part, a movement sensor means to detect the movement of the movable part on a flat surface and a plurality of function keys. The computer mouse can encode the status of the function keys and the relative position and movement thereof on an X-Y plane and send the resulting codes to the computer via a communication port, such as an RS-232C interface. The computer then moves the cursor and performs different operations in accordance with the received codes.
The movement sensor means is used to determine the velocity of the movable part, including its speed and direction. The movement sensor means is generally categorized into two groupings, mechanical and optical. In the mechanical movement sensor, the rolling movement of a tracking ball on a flat surface actuates a grid and thus intermittently turns on and off a photocoupler. The resulting analog signal is then amplified and conditioned so as to become a digital signal. In the optical movement sensor, optical elements are provided so as to emit light signals which, after being reflected by a grid pad, will be received and encoded by a rotary encoder so as to be obtain electric signals.
The photoelectric elements and analog amplifying and conditioning circuits which are used in the above-mentioned movement sensors consume a great amount of energy. This is very uneconomical, especially for a computer mouse which is connected to an RS-232C interface, for a cordless mouse or for a computer mouse of a lap-top computer.
Furthermore, in a conventional computer mouse, the grid receives a great number of noise signals when it is partially closed. These noise signals are often mistaken for movement signals by the computer mouse, and frequent, untimely movement of the cursor on the computer display screen therefore occurs. The frequent unwanted movement of the cursor also results in greater energy consumption.